The rabbit is a good animal model for the study of many human diseases because of its anatomical, genetic and biochemical similarities to the human. It is also used for drug screening, production of antibody and production of therapeutic proteins. The rabbit is large enough to provide adequate quantities of tissue for experimental work, produce sufficient amount of antibody or therapeutic proteins, and yet it is small enough to be economical for most laboratories. To date, pronuclear microinjection remains the primary method to produce transgenic rabbits. There are no germline competent rabbit embryonic stem (rbES) cell lines available. Pronuclear microinjection, however, is of low efficiency, results in random integration, and cannot produce gene targeted transgenic animals. The purpose of this SBIR project is to establish germline competent rbES cell lines for the production of gene targeted transgenic rabbits. In Phase I we established rabbit embryonic fibroblasts as feeder layers, synthesized recombinant rabbit leukemia inhibitory (LIF) factor, and derived putative rbES cells. In Phase II, we will work to validate if these rbES cells can contribute to germ line cells after blastocyst injection and we will work to produce gene targeted transgenic rabbits from these cells. Specific Aims in Phase II project include: (1) derive new rbES cell lines with inhibitors of differentiation;(2) evaluate germline competency of rbES cells;and (3) produce gene targeted transgenic rabbits. The success of this project will establish the first germline competent ES cell lines in a non-murine species, improve the transgenic efficiency in rabbits, and make the production of gene targeted rabbits possible. PUBLIC HEALTH RELEVANCE: The rabbit is a good animal model for the study of many human diseases because of its anatomical, genetic and biochemical similarities to the human. It is also used for drug screening, production of antibody and production of therapeutic proteins. The main reason that rabbit has not been in these fields is that there have been no established germline competent rabbit embryonic stem (rbES) cell lines. The success of this project will establish the first germline competent ES cell lines in a non-murine species, improve the transgenic efficiency in rabbits, and make the production of gene targeted rabbits possible.